The goal of this clinical trial is to learn how 24 IU oxytocin (OT) and 24 IU arginine vasopressin (AVP), administered through the oral mucosa, affect attention to emotional faces and related brain activity in healthy adults. The study will compare OT and AVP with a placebo (PLC).
The main questions it aims to answer are:
1. Does oromucosally administered oxytocin produce a behavioral pattern of modulation of top-down and bottom-up attention to emotional faces that is qualitatively consistent with previously reported intranasal oxytocin effects, and how does this pattern compare with that produced by arginine vasopressin? 2. Do oromucosally administered oxytocin and arginine vasopressin modulate neural responses within predefined brain regions and networks involved in emotional salience, attentional control, and social information processing, and are these neural effects consistent with their behavioral effects? 3. Do oxytocin and arginine vasopressin show overlapping or distinct patterns of neural modulation across top-down and bottom-up attention and high and low attentional load conditions? Researchers will compare 24 IU OT and 24 IU AVP with a placebo to determine how these treatments influence emotional face attention and brain activity.
Participants will:
* Receive 24 IU OT, 24 IU AVP, or placebo via a lyophilized oromucosal lollipop * Allow the treatment to be absorbed through the oral mucosa for about 5 minutes * Provide blood samples before and after treatment to assess peripheral oxytocin and vasopressin levels * Complete emotional face attention tasks during fMRI scanning * Have response time, response accuracy, brain activity, and peripheral neuropeptide levels measured * Complete questionnaires assessing mood states and personality traits before treatment administration to control for potential confounding effects
Healthy subjects without past or current psychiatric or neurological disorders
Normal or corrected-to-normal vision
Eligible for MRI scanning and willing to undergo blood sampling and study treatment administration
For naturally cycling female participants, willingness and ability to complete the experimental session within the predefined menstrual-cycle phase, determined using menstrual history and urinary luteinizing hormone (LH) testing
History of head injury or epilepsy or seizure disorders
Current or past major psychiatric, neurological, or serious medical illness that may affect participant safety or study outcomes
Current use of psychoactive medications, hormonal medications, or other medications that may substantially affect central nervous system or neuroendocrine function
Regular smoking or inability to comply with the required nicotine abstinence period before testing
Parallel
Oxytocin (OT)
DrugA single dose of 24 IU oxytocin (OT) is administered via a lyophilized oromucosal lollipop. Participants are instructed to continuously lick the lollipop for approximately 5 minutes to facilitate absorption through the oral mucosa and not to bite, chew, or directly swallow it.
Arginine Vasopressin (AVP)
DrugA single dose of 24 IU arginine vasopressin (AVP) is administered via a lyophilized oromucosal lollipop. Participants are instructed to continuously lick the lollipop for approximately 5 minutes to facilitate absorption through the oral mucosa and not to bite, chew, or directly swallow it.
Placebo (PLC)
DrugPlacebo (PLC), consisting of lyophilized normal saline, is administered via a matched oromucosal lollipop using the same administration procedure as the active treatments. The placebo lollipop is matched to the OT and AVP lollipops in appearance, powder characteristics, and taste.
Behavioral Performance in the Emotional Face Attention Tasks
Behavioral performance will be assessed using correct response time and response accuracy during the emotional face attention tasks. Analyses will examine treatment-related effects across the oxytocin (24 IU), arginine vasopressin (24 IU), and placebo groups within the top-down and bottom-up attention tasks and under high and low attentional load. Primary analyses will evaluate treatment effects and treatment-by-task-condition interactions on reaction time and accuracy. Direct comparisons among OT, AVP, and placebo will be used to characterize shared and differential behavioral effects of the two neuropeptides. For oxytocin, the behavioral effects observed following oromucosal administration will be interpreted with reference to previously reported intranasal findings using the same or a conceptually related attentional framework. Particular emphasis will be placed on whether the direction and condition dependence of effects on reaction time and accuracy show qualitative consistency.
BOLD Responses in Predefined Brain Regions and Networks
Task-evoked BOLD responses will be measured using fMRI during the emotional face attention tasks. Primary neuroimaging analyses will examine treatment-related effects within predefined regions of interest and neural networks implicated in emotional salience, attentional control, emotional face processing, and social neuropeptide processing. Regions of interest will be defined independently of the present treatment effects using anatomical definitions and/or prior literature. Treatment effects and treatment-by-task-condition interactions will be assessed across the oxytocin, arginine vasopressin, and placebo groups during top-down and bottom-up attention and under high and low attentional load. Complementary whole-brain analyses will be conducted to identify treatment-related neural effects outside the predefined regions and to characterize broader patterns of task-evoked modulation.
Peripheral Oxytocin and Arginine Vasopressin Levels
Peripheral oxytocin and arginine vasopressin concentrations will be measured from blood samples collected before and after treatment administration to assess treatment-related changes in circulating neuropeptide levels.
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